1. Field of Invention
The invention relates to a photoinitiator and a preparation method thereof and in particular to a bisbiphenylacylphosphine oxide and its preparation method.
2. Related Art
A photoinitiator is a spectacular compound that can absorb a specific wavelength of photo energy to release free radicals by a cleavage or β cleavage. Therefore it can be used as an initiator for a monomer chain reaction. Most photoinitiators have the properties of low price, good stability, no toxicity, no colorizing, easy to make, long life span free radical and good light absorption rate. Recently, the demand for its application has driven the development of low energy and long wavelength light initiators, with most of the initiators consisting of a carbonyl chromophoric group. In a light wavelength range of 300 nm to 400 nm and based on the Norrish Type I, a photoinitiator of biphenylacryphosphine oxide can directly release free radicals without the assist of a sensitizer, so that it can be directly used for polymerizing acrylics.
Most of the acryphosphine oxides such as those disclosed in U.S. Pat. Nos. 5,407,969, 5,008,426 and European patent 413657 belong to an aliphatic group, a phenyl group or a monophenylacryphosphine oxide and have remarkable effects in practice. However, the light initiator compound should have greater equivalent to make the polymerization more efficient. Thus, how to develop a high equivalent compound for a light initiator has become an important topic in the field.